//! XAudio render-driver-client registration + buffer-complete callback loop
//! (canary parity: `xenia/apu/audio_system.cc`).
//!
//! Replaces the host-thread + per-client-semaphore + XAudio2 driver layer with
//! a periodic ticker that enqueues a "buffer complete" fire for each
//! registered client at the audio frame rate (256 samples / 48 kHz ≈ 5.33 ms).
//! The injection path in `xenia-app` reuses the same [`crate::SavedCallbackCtx`]
//! plumbing the graphics-interrupt path uses — only one callback runs at a
//! time across either subsystem, gated by `interrupts.is_in_callback()`.
//!
//! Lockstep mode uses an instruction-count proxy
//! ([`XAUDIO_INSTR_PERIOD`]) so `--stable-digest` stays bit-exact;
//! `--parallel` uses wall-clock ([`XAUDIO_PERIOD`]) — same dual-mode pattern
//! as KRNBUG-D08 v-sync.

use std::collections::VecDeque;
use std::time::{Duration, Instant};

/// Mirrors [audio_system.h:30](../../../../xenia-canary/src/xenia/apu/audio_system.h#L30)
/// `kMaximumClientCount = 8`.
pub const XAUDIO_MAX_CLIENTS: usize = 8;

/// Source code stamped into [`crate::SavedCallbackCtx::source`] when an
/// audio callback is injected. Distinct from graphics-interrupt sources
/// (`INTERRUPT_SOURCE_VSYNC = 0`, `INTERRUPT_SOURCE_CP = 1`) so logs and
/// the audit trail can disambiguate.
pub const INTERRUPT_SOURCE_AUDIO: u32 = 0x100;

/// Lockstep instruction-count period. Picked so the ratio against
/// [`crate::interrupts::VSYNC_INSTR_PERIOD`] (`150_000`) ≈ 16.67 ms / 5.33 ms,
/// matching canary's 256 samples / 48 kHz audio cadence.
pub const XAUDIO_INSTR_PERIOD: u64 = 48_000;

/// Wall-clock period under `--parallel`. 256 / 48000 s = 5.333… ms.
pub const XAUDIO_PERIOD: Duration = Duration::from_nanos(5_333_333);

/// Bound on the pending-fires FIFO. Stops a long-running export from
/// queueing unbounded callbacks while injection is starved.
pub const XAUDIO_QUEUE_CAP: usize = 16;

#[derive(Debug, Clone, Copy)]
pub struct XAudioClient {
    pub callback_pc: u32,
    pub callback_arg: u32,
    /// Guest pointer to the heap-allocated 4-byte buffer holding
    /// `callback_arg` big-endian — passed as r3 to the guest callback,
    /// matching canary's
    /// [audio_system.cc:225-228](../../../../xenia-canary/src/xenia/apu/audio_system.cc#L225-L228)
    /// + [audio_system.cc:139-141](../../../../xenia-canary/src/xenia/apu/audio_system.cc#L139-L141).
    pub wrapped_callback_arg: u32,
}

#[derive(Debug)]
pub struct XAudioState {
    pub clients: [Option<XAudioClient>; XAUDIO_MAX_CLIENTS],
    pub pending: VecDeque<usize>,
    pub delivered: u64,
    pub dropped: u64,
    pub accumulator: u64,
    pub last_instr_count: u64,
    pub last_instant: Option<Instant>,
}

impl Default for XAudioState {
    fn default() -> Self {
        Self {
            clients: [None; XAUDIO_MAX_CLIENTS],
            pending: VecDeque::new(),
            delivered: 0,
            dropped: 0,
            accumulator: 0,
            last_instr_count: 0,
            last_instant: None,
        }
    }
}

impl XAudioState {
    pub fn register(&mut self, client: XAudioClient) -> Option<usize> {
        for (i, slot) in self.clients.iter_mut().enumerate() {
            if slot.is_none() {
                *slot = Some(client);
                return Some(i);
            }
        }
        None
    }

    pub fn unregister(&mut self, index: usize) {
        if index < XAUDIO_MAX_CLIENTS {
            self.clients[index] = None;
            self.pending.retain(|&i| i != index);
        }
    }

    pub fn get(&self, index: usize) -> Option<XAudioClient> {
        self.clients.get(index).copied().flatten()
    }

    pub fn any_registered(&self) -> bool {
        self.clients.iter().any(|c| c.is_some())
    }

    fn enqueue_all_active(&mut self) {
        for i in 0..XAUDIO_MAX_CLIENTS {
            if self.clients[i].is_none() {
                continue;
            }
            if self.pending.len() >= XAUDIO_QUEUE_CAP {
                self.dropped += 1;
                return;
            }
            self.pending.push_back(i);
        }
    }

    pub fn peek_next(&self) -> Option<usize> {
        self.pending.front().copied()
    }

    pub fn take_next(&mut self) -> Option<usize> {
        self.pending.pop_front()
    }

    /// Lockstep instruction-count ticker. Idempotently advances the
    /// accumulator from `last_instr_count` to `current_instr_count` and
    /// enqueues one fire-set per full [`XAUDIO_INSTR_PERIOD`] crossed.
    /// Returns `true` iff at least one fire was queued.
    pub fn tick_instr(&mut self, current_instr_count: u64) -> bool {
        if !self.any_registered() {
            self.last_instr_count = current_instr_count;
            self.accumulator = 0;
            return false;
        }
        let delta = current_instr_count.saturating_sub(self.last_instr_count);
        self.last_instr_count = current_instr_count;
        self.accumulator = self.accumulator.saturating_add(delta);
        if self.accumulator < XAUDIO_INSTR_PERIOD {
            return false;
        }
        let periods = self.accumulator / XAUDIO_INSTR_PERIOD;
        self.accumulator %= XAUDIO_INSTR_PERIOD;
        let to_fire = (periods as usize).min(XAUDIO_QUEUE_CAP);
        for _ in 0..to_fire {
            self.enqueue_all_active();
        }
        true
    }

    /// Wall-clock ticker for `--parallel`. First call seeds the anchor
    /// (no fire). Subsequent calls fire `floor(elapsed / XAUDIO_PERIOD)`
    /// fire-sets and advance the anchor by that many full periods.
    pub fn tick_wallclock(&mut self) -> bool {
        if !self.any_registered() {
            self.last_instant = None;
            return false;
        }
        let now = Instant::now();
        let anchor = match self.last_instant {
            Some(t) => t,
            None => {
                self.last_instant = Some(now);
                return false;
            }
        };
        let elapsed = now.saturating_duration_since(anchor);
        let period_ns = XAUDIO_PERIOD.as_nanos() as u64;
        let elapsed_ns = elapsed.as_nanos() as u64;
        let periods = elapsed_ns / period_ns;
        if periods == 0 {
            return false;
        }
        let advance = Duration::from_nanos(periods * period_ns);
        self.last_instant = Some(anchor + advance);
        let to_fire = (periods as usize).min(XAUDIO_QUEUE_CAP);
        for _ in 0..to_fire {
            self.enqueue_all_active();
        }
        true
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    fn dummy_client(arg: u32) -> XAudioClient {
        XAudioClient {
            callback_pc: 0x8200_0000 + arg,
            callback_arg: arg,
            wrapped_callback_arg: 0x4000_0000 + arg,
        }
    }

    #[test]
    fn register_assigns_first_free_slot() {
        let mut s = XAudioState::default();
        let i0 = s.register(dummy_client(1)).unwrap();
        let i1 = s.register(dummy_client(2)).unwrap();
        assert_eq!(i0, 0);
        assert_eq!(i1, 1);
        assert_eq!(s.get(0).unwrap().callback_arg, 1);
        assert_eq!(s.get(1).unwrap().callback_arg, 2);
    }

    #[test]
    fn unregister_clears_slot_and_pending() {
        let mut s = XAudioState::default();
        let i = s.register(dummy_client(1)).unwrap();
        s.pending.push_back(i);
        s.unregister(i);
        assert!(s.get(i).is_none());
        assert!(s.pending.is_empty());
    }

    #[test]
    fn register_returns_none_when_full() {
        let mut s = XAudioState::default();
        for k in 0..XAUDIO_MAX_CLIENTS {
            assert!(s.register(dummy_client(k as u32)).is_some());
        }
        assert!(s.register(dummy_client(99)).is_none());
    }

    #[test]
    fn tick_instr_no_clients_does_not_fire() {
        let mut s = XAudioState::default();
        assert!(!s.tick_instr(XAUDIO_INSTR_PERIOD * 10));
        assert!(s.pending.is_empty());
    }

    #[test]
    fn tick_instr_fires_at_period() {
        let mut s = XAudioState::default();
        let i = s.register(dummy_client(7)).unwrap();
        assert!(!s.tick_instr(XAUDIO_INSTR_PERIOD - 1));
        assert!(s.pending.is_empty());
        assert!(s.tick_instr(XAUDIO_INSTR_PERIOD));
        assert_eq!(s.peek_next(), Some(i));
    }

    #[test]
    fn tick_instr_drains_multiple_periods_in_one_call() {
        let mut s = XAudioState::default();
        let i = s.register(dummy_client(7)).unwrap();
        assert!(s.tick_instr(XAUDIO_INSTR_PERIOD * 4));
        assert_eq!(s.pending.len(), 4);
        for _ in 0..4 {
            assert_eq!(s.take_next(), Some(i));
        }
        assert!(s.pending.is_empty());
    }

    #[test]
    fn tick_instr_fires_for_each_registered_client() {
        let mut s = XAudioState::default();
        let a = s.register(dummy_client(1)).unwrap();
        let b = s.register(dummy_client(2)).unwrap();
        assert!(s.tick_instr(XAUDIO_INSTR_PERIOD));
        assert_eq!(s.pending.len(), 2);
        assert_eq!(s.take_next(), Some(a));
        assert_eq!(s.take_next(), Some(b));
    }

    #[test]
    fn tick_instr_caps_queue_growth() {
        let mut s = XAudioState::default();
        s.register(dummy_client(1)).unwrap();
        s.tick_instr(XAUDIO_INSTR_PERIOD * (XAUDIO_QUEUE_CAP as u64 + 50));
        assert!(s.pending.len() <= XAUDIO_QUEUE_CAP);
    }

    #[test]
    fn tick_wallclock_first_call_seeds_anchor() {
        let mut s = XAudioState::default();
        s.register(dummy_client(1)).unwrap();
        assert!(!s.tick_wallclock());
        assert!(s.pending.is_empty());
        assert!(s.last_instant.is_some());
    }

    #[test]
    fn tick_wallclock_fires_after_period() {
        let mut s = XAudioState::default();
        let i = s.register(dummy_client(1)).unwrap();
        s.tick_wallclock();
        std::thread::sleep(XAUDIO_PERIOD + Duration::from_millis(2));
        assert!(s.tick_wallclock());
        assert!(!s.pending.is_empty());
        assert_eq!(s.peek_next(), Some(i));
    }
}